Measurement of the formation and evolution of a strange attractor in a laser

We have measured the fractal dimensions and the Kolmogorov entropies of periodic and chaotic attractors for a ${\mathrm{CO}}_2$ laser system with modulated losses. In particular, we find an increase in dimension near the accumulation point of the periodic cascade according to the Feigenbaum scaling law, besides the expected usual increase of the attractor dimension in the chaotic region. Numerical solutions of the theoretical model yield dimensions in quantitative agreement with the experiments, thus demonstrating a close match of experiment and theory for this physical system.